Solid hypergolic propellant systems

ABSTRACT

Hypergolic solid oxidizer and fuel systems are provided whereby ignition and combustion of the separate solid fuel and oxidizer grains can be obtained by contacting of the respective grains. Suitable solid oxidizers include NOBrF4, LiClO4 . NOF, MgClO4 . 2NOF, NO2ClO4, NO2BF4, (NO2)3 (AlClO4)6, NO2AsF6, NO2SbF6, and NO2PF6. Suitable solid fuels include LiAlH4, LiBH4, Li2AlH5, BeH2, LiH2 . BeH2, tetramethylammonium hydrotriborate, triaminoguonidinium diazine, diaminotetrazine, 4-amino-3, 5dihydrazine-1,2,4-triazole, N2H4(BH3)2, Mu (hydrazino)decaborane, 3,6-dihydrazine-s-tetrazine, NH4N3, (CH3)4NB3H8 and borane complexes with ammonia such as B10H12 . 2NH3. Completely fluorinated polyethylene resin is a suitable binder for the oxidizer system.

United States Patent [191 Iwanciow et al.

[ SOLXD HYPERGOLIC PROPELLANT SYSTEMS [75] Inventors: Bernard L.lwanciow, Sunnyvale;

William J. Lawrence, San Jose, both of Calif.

United Aircraft Corporation, East Hartford, Conn.

[22] Filed: June 4, 1965 [21] Appl. No.: 461,555

[73] Assignee:

[52] US. Cl. 60/219, 149/19, 149/20, 149/22, 149/36, 149/74 [51-] Int.Cl C06d 5/06 [58] Field of Search 149/2, 22, 19, 20, 74, 149/36; 60/219[56] References Cited UNITED STATES PATENTS 4/1961 Barnes 149/2 UX9/1963 Olah et a1. 7/1964 Olah 60/219 [451 Mar. 19, 1974 Gluckstein 1149/2 X Burke et a1. 149/19 X Primary ExaminerBenjamin R. Padgett 5 7ABSTRACT Hypergolic solid oxidizer and fuel systems are provided wherebyignition and combustion of the separate solid fuel and oxidizer grainscan be obtained by triaminoguonidinium diazine, diaminotetrazine, 4-

amino-3, 5-dihydrazine-1,2,4-triazole, N H (BH',LL(hydrazino)decaborane, 3,6-dihydrazine-s-tetrazine, N1-1 N (Cl-l hNBl-l and borane complexes with ammonia such as B H 2Nl-1 Completelyfluorinated polyethylene resin is a suitable binder for the oxidizersystem.

8 Claims, No Drawings SOLID HYPERGOLIC PROPELLANT SYSTEMS This inventionrelates to hypersolid combustion systems and, more particularly, to anovel hypersolid oxidizer and fuel composition. The term hypersolidrelates to a system in which solid oxidizer bodies and solid fuel bodiesare hypergolic with respect to each other. The broad concept of usingsuch systems as heat and light generators as well as thrust generatorsis described in co-pending application Ser. No. 328,156 filed Nov. 29,1963 by lwanciow and MacLaren. The aforementioned application disclosesthat a hypergolic system can be formed when alkali metal hydrides areemployed as fuels and solid interhalogen alkali metal fluorides areemployed as oxidizers by forming the fuel and oxidizer materials intoseparate solid grains. When the grains are controllably brought intocontact, a controllable combustion process is produced. A steady statecombination process can be maintained by feeding the grains together ata constant predetermined rate. Merely by separating the two grains, theprocess can be stopped and combustion may be reinitiated by againbringing the grains together. Such systems have great utility as heatgenerators where the hot combustion gas can be used to turn a turbine orpassed over heat exchange coils; as light generators wherein thehypersolid pairs can be substituted for the carbon arc source in searchlights for example, and as thrust generators when the hypersolid pairsare combusted within a reaction motor and the combustion gas isexhausted through a suitable nozzle. Subsequent work, both experimentaland theoretical, has led to a more complete understanding of the processof hypergolic solid combustion. This process requires that the fuel andoxidizer species react spontaneously when they are brought into intimatephysical contact. This reaction is an ignition process that leads to asteady state combustion condition when the fuel and oxidizer elementsare advanced at a con stant rate. When the advancement of the elementceases or reverses in direction, the combustion process terminates. Thistype of behavior places very stringent requirements upon the physicaland chemical nature of the compounds that may be successfully employed.The ignition phenomena must, of necessity, be a reaction whose energy ofactivation is extremely low. This energy is to be supplied by merelyphysically contacting the elements. In some cases, slight contact issufficient to cause ignition and, in other cases, a higher degree ofphysical contact is required and is obtained by pressure on thecontacting surfaces or by agitation of the contacting surfaces.

In addition, the reaction must supply sufficient energy to result in agasification of fuel and oxidizer species from their respectivesurfaces. The transport dynamics require that the solids possess asufficiently low thermal diffusivity which will not allow dissapation ofthe energy as sensible heat at a rate which limits the gasificationprocess. In addition, the propellant elements must have sufficientstrength and physical integrity to insure that mechanical failure doesnot occur on contact. Therefore, the chemical nature of the elements andtheir physical properties must be such that neither the oxidizer nor thefuel species exhibits monopropellant tendencies or are capable of selfdegradation when raised to temperatures that will exist at the solidsurface during steady state combustion. In addition, impact or shocksensitive materials are undesirable from both this standpoint and fromthe standpoint of use of the materials as propellant compositions inrocket motors. Further, the materials must have adequate thermal andphysical properties such that the formation of a significant melt zonewill not occur. A significant melt zone at the interface could causeoperational difficulties as a result of the loss of grain integrity.Fuel and oxidizer systems other than those disclosed in the above patentapplication are described in U.S. Pat. Nos. 3,103,782 and 3,141,295.

Presently, both the fuel and oxidizer grains are fabricated bycompression molding techniques. Consequently, in addition to theproperties described above, the particular oxidizer and fuel speciesemployed must also lend themselves to fabrication by this technique.Considerable difficulty has been encountered in ob taining satisfactorypressing with the oxidizers and fuels described in the aforementionedpatent application. In particular, uniform compaction is not alwaysachieved resulting in poor grain integrity and, in some cases, grainfracture occurs on ejection of the pressing from the die. One of theproblems at present is to achieve all the desired physical and chemicalproperties described above in a single grain.

According to this invention, we have discovered a new group of oxidizerand fuel materials which are hypergolic with respect to each other. Wehave also invented compositions containing both these new materials andthe materials previously disclosed that exhibit improved physicalcharacteristics.

It is, accordingly, a primary object of this invention to provide a newclass of solid oxidizer and fuel materials that exhibit hypergolicproperties.

It is a further object of this invention to provide a source ofcombustion gases utilizing these new classes of hypergolic solidmaterials.

It is another object of this invention to improve the physicalcharacteristics of hypersolid oxidizer and fuel grains.

These and other objects of this invention will be readily apparent fromthe following disclosure.

In view of the characteristics we determined to be necessary for thesuccessful operation of a hypergolic solid system, the following broadparameters are considered to generally define the nature of the fuel andoxidizer species. Since the activation energy of the reaction isproduced solely by intimate contact of the materials, oxidizers of astrongly acidic nature should be used in conjunction with basic fuelssince acid-base reactions possess relatively low activation energies.Secondly, the products of this initial reaction should be capable ofoxidative reaction to produce a high temperature for continuouscombustion and the generation of heat, light and hot combustion gases.Since most oxidation-reduction reactions have relatively high activationenergies, the approach is to use oxidizer-fuel pairs which undergo anacid-base reaction to supply the activation energy for a redox reaction.

As oxidizer components, we have discovered a large number of materialsother than the metallic complex fluorides of the prior art and theaforementioned patent application that function in hypergolicsolidsystems. These oxidizers are nitrosyl and nitronium compounds andcomplexes thereof with metallic perchlorates. Preferred compoundsconsist of nitrosyl tetrafluorobr0- mate (NOBrF and complexes of lithiumperchloroate and magnesium perchlorate with nitrosyl fluoride (LiClO NOFand MgClO 2NOF). The preferred nitronium compound is nitroniumperchlorate (N C10 but other compounds such as nitronium aluminumchlorate [(NO (AlClO nitronium tetrafluoroborate (NO BF nitroniumhexafluoroarsenate (NO AsFs), nitronium hexafluoroantimionate (NO SbFand nitronium hexafluorophosphate LiAll-h, LiBH Li All-l Bel-l LiH BeHtetramethylammonium hydrotriborate, triaminoguonidinium diazide,diaminotetrazine, 4-

amino-3,5-dihydrazinol ,2,4-triazole, N H Bl-l andu-(hydrazino)decaborane, 3,o-dihydrazino-s-tetrazine, NH N (Cl-l NB Hand borane complexes with ammonia B H -2 NH Example 1 Granular nitroniumperchlorate was added to granules of (CH NH H A hypergolic combustionoccurred upon application of slight pressure of the materials producinga maximum temperature estimated at 3,788K with a maximum theoreticalspecific impulse of 295 seconds. Example 2 The procedure of Example Iwas repeated, substituting LiAlH, for (CH NB H hypergolic combustionoccurred upon application of pressure to the materials producing amaximum temperature estimated at 4,250K and theoretical specific impulseof 300 seconds. Example 3 The procedure of Example 2 was repeatedsubstituting B l-l, (Nl-l for LiAlH Hypergolic combustion was obtainedupon vigorous stirring of the granules to provide intimate contact. Amaximum temperature of 4,1 10K was estimated with a theoretical specificimpulse of 287 seconds. The procedure of Example 3 was repeated using Bl-l 2NH tetramethylammonium hydrotriborate, amino dihydrazino triazole,dihydrazino tetrazine and solid mixture comprising 25% Li, 25% Lil-l,37.5 percent polyethylene and 12.5 percent polypropylene-glycol. All thesystems exhibited hypergolic combustion upon vigorous stirring of thegranules. Example 4 Granules of NOBrF, were added to granules of (Cl-l)NB H and hypergolic combustion occurred upon contact of the materials.Example 5 Cast granules of a 50-50 mixture of triaminoguanidiniumdiazide and polyethylene were used as fuel in the procedure of Example 4and hypergolic combustion occurred on contact.

Example 6 Granules of NOBrE, were added to granules of B H1z(NH andhypergolic combustion occurred on contact of the materials. Thisprocedure was repeated using LiAlH, as a fuel and hypergolic combustionoccurred upon application of slight pressure to the material. The aboveexamples are illustrative of hypergolic combustion of representativenitronium and nitrosyl compounds with a wide variety of fuel materials.The

above procedure can be repeated with combinations of the hereinbeforedefined fuels and oxidizers of this invention and hypergolic combustioncan be produced.

Up to this point, the invention has been described with respect to thesimplest form of hypergolic system in which granules of the fuel andoxidizer are physically mixed. Such systems are useful in the batch-wiseproduction of heat and light and in continuous systems wherein thegeneration of heat and light is regulated by controlling the mixing rateof the materials. In such systems the physical properties of thegranules are not too important since the entire granule is consumed in arelatively short time. However, when the fuel and oxidizer are formedinto separate grains and the combustion process controlled by regulatingthe rate at which the grains are fed together, as hereinbeforedescribed, the physical properties of the materials assume greaterimportance.

Propellant candidates have been found which have ideal hypergolicproperties, but fall short with respect to the thermal or physicalproperties when compressed into grains. Cesium hexafluorobromate(CSBI'FS) is a good example to illustrate this point. Its ignitioncharacteristics are ideal, but it has a tendency to melt under steadystate combustion conditions. Nitronium perchlorate, on the other hand,has adequate physical and thermal properties, but has exhibiteddifficulties in promoting easy ignition with many candidate fuels whencompressed into a grain. The use ofa binder to improve the physicalcharacteristics of the fuel and oxidizer grains was considered.Considerable difficulty was encountered in using a binder, particularlywith respect to the oxidizer, the more reactive of the components. Sincemost binders for fuel compositions also comprise substances that willburn once combustion has started, the choice of a fuel binder is not ascritical. The oxidizer binder, however, must be compatible with theoxidizer and not cause the oxidizer grain to have monopropellantcharacteristics. Further, if a binder is used with the oxidizer grain,the material used and the amounts used must not impede the hypergolicityof the system. Prior to our discovery, no single chemical species hasexhibited the desired chemical and physical properties as well as thenecessary hypergolicity.

We have found that by incorporating a completely halogenatedpolyethylene resin (i.e., Teflon) into the oxidizer grain in amounts upto approximately 12 percent, a grain having hypergolic properties withrespect to the aforementioned fuels can be produced which has thedesired physical properties. The following examples are illustrative ofthis aspect of the invention.

Example 7 Finely divided nitronium perchlorate, cesium hexafluorobromateand Teflon were thoroughly mixed in proportions, by weight, of 64percent nitronium perchlorate; 27 percent cesium hexafluorobromate; and9 percent Teflon, the mixture was compacted under 10,000 psi pressure atF temperature. The resultant grain in the form of a cylinder 1 inch indiameter was ejected from the die and examined for physical defects. Nograin fractures were observed. A composite fuel grain comprising weightper cent B l-l ZNH and 20 weight percent polyethylene was also compactedin a die to form 1 inch cylindrical grain. This grain was also ejectedfrom the die and examined for physical defects. No grain fractures wereobserved. The Teflon employed in manufacturing the oxidizer grain wasAllied Chemical Companys HALON TEF TYPE G-SO and polyethylene was AlliedChemical Companys ultrahigh molecular weight polyethylene TYPE AC 1220.The fuel and oxidizer grains were mounted in a hypergolic combustiondevice which permits the grains to be fed together at a constantcontrollable rate. The grains were physically contacted and ignitionoccurred. The grains were then fed at constant rates varying from 0.02inch per second to 0.37 inch per second and stable combustion wasmaintained throughout the range of feed rates. The combustion processwas terminated both by withdrawing grains from each other and bydecreasing the feed rate to below 0.02 inch per second. In the lattercase, the combustion process continued until the separation of thegrains was so great that the heat transfer and mass transfer processescould no longer sustain combustion. Reignition was obtained by bringingthe grains once more into contact. Upon completion of a test cycle, thegrains were examined for physical defects and were found to be intactand capable of subsequent reignition.

Example 8 An oxidizer grain was formed from 78 percent nitroniumperchlorate, balance cesium hexafluorobromate compressed into a 1 inchgrain. The fuel grain was the same as in Example 1. The two grains weremounted in the hypergolic combustion apparatus and ignited as inExample 1. A feed rate of 0.03 inch per second was used on a testburning time of 7.2 seconds. A post-firing inspection of the oxidizergrain revealed longitudinal cracking in several places in the vicinityof the contacting surface. The surface was also jagged and severalfragments of the oxidizer were found in the bottom of the combustionapparatus. Apparently the oxidizer grains integrity was compromised as aresult of thermal expansion and contraction experienced during theignition combustion and termination of the combustion. In the aboveexamples, CsBrFfi is incorporated as an ignition aid, but is notessential. Ignition will occur without CsBrF if sufficient pressure oragitation of the grain is utilized.

A series of tests were run to determine the operating characteristics ofother systems wherein Teflon is employed as a binder for the oxidizergrain. The result of a portion of these experiments is tabulated inTable 1. As can be seen from Table l, the oxidizer-Teflon composition iscompatible with several hypergolic fuel systerns. The maximum per centof Teflon that may be employed without impairing the hypergolicityvaries with the systems, but appears to be a maximum of about 12percent. Above this amount of Teflon, no system exhibits hypergolicity.Of course, it is not desirable to utilize the maximum amount of Teflonsince the inclusion of this material with the oxidizer tends to reducethe specific impulse of the system. The best results were obtained inusing weights of Teflon from about 9 percent to about 1 1.3 percent.Below 9 percent, the binding effeet and the improvement of the physicalcharacteristics drop off rapidly and below approximately 5 percentTeflon, there is no notable improvement in the thermal characteristicsTABLE 1 Test (wt Oxidizer Fuel Comp Results No. Comp 1 79.8% NO,C1O B H'2NH, Ignition with slight agitation l 1.3% Teflon 8.9% CsBrF 2 72.7%No,ClO B H -ZNH, Ignition with slight agitation 9.1% Teflon 18.2% CsBrF3 64.0% No,ClO B H 'ZNH Ignition on slight pressure 9.0% Teflon 27.0%CsBrF 4 79.8% NO C1O Tetramethylam- Ignition on vigorous moniumagitation hydrotriborate 1 1.3% Teflon 8.9% CsBrF 5 64.0% NO CIOTetramethylam- Ignition on vigorous monium agitation hydrotriboratc 9.0%Teflon 27.0% BrF 6 64.0% NO CIO Amino Ignition on vigorous Dihydrazinoagitation Triazol 9.0% Teflon 27.0% CsBrF 7 79.0% NO CIO DihydrazinoIgnition on vigorous Tetrazine agitation 1 1.3% Teflon 8.9% CsBrF 864.0%NO,CIO Dihydrazino Ignition on vigorous Tetrazine agitation 9.0%Teflon 27.0% CsBrF and physical properties of the grains. The tabulatedresults relate to experiments using nitronium perchlorate as the primaryoxidizer; however, the use of Teflon as a binder in grains of theaforementioned oxidizers will also produce a grain having improvedphysical properties.

This invention has been disclosed with respect to various specificexamples; however, these examples are i1- lustrative rather thanlimiting. The invention includes various obvious modifications andsubstitutions and is limited solely by the following claim. claims.

We claim:

1. In a process for producing hypergolic combustion which comprisesproviding a solid oxidizer grain and a solid fuel grain, said oxidizerand fuel being members of an acid-base pair capable of generatingsufficient energy from an acid-base reaction to activate anoxidation-reduction reaction between said oxidizer and fuel, and placingsaid oxidizer grain and fuel grain in intimate contact for sufficienttime to initiate said oxidation-reduction reaction, the improvementwherein said oxidizer grain comprises a material selected from the groupconsisting of NOBrF LiClO, NOF, MgCIO, ZNOF, NO ClO (NO (AlCl04)6, NO-AsF NO SbF and NO PF 2. The process of claim 1 wherein said oxidizergrain contains an ignition aid comprising an alkali metalhexafluorobromate.

3. The process of claim 1 wherein said oxidizer grain contains from 5 to12 percent by weight of a totally fluorinated polyethylene resin.

4. A hypergolic solid oxidizer grain consisting essentially of 64% NOClO 27% CsBrl}; and 9 percent totally fluorinated polyethylene.

5. The process of claim 1 wherein said fuel grain comprises a materialselected from the group consisting of metal hydrides,tetramethylammonium hydrotriborate, diaminotetrazine,4-amino-3,5-dihydrazino-1,2,4 triazole, N H,,( BH n-(Hydrazino)decaborane, 3,fi-dihydrazino-s-tetrazine, NH N triaminoguanidiniumdiazide, (Cl-l NB l-l and B H 2Nl-l 6. The process of claim wherein thefuel grain contains up to 50 percent by weight of polyethylene as abinder.

7. In a method for producing thrust from a reaction motor whichcomprises providing a solid oxidizer grain and a solid fuel grain withinsaid reaction motor, said oxidizer and said fuel being members of anacid base pair capable of generating sufficient energy from an acid basereaction to active an oxidation-reduction reaction between said oxidizerand fuel; placing said oxidizer and fuel grains in intimate contactwithin said reaction motor for sufficient time to initiate saidoxidation-reduction reaction whereby gaseous combustion products areproduced within said reaction motor and exhausting said gaseouscombustion products from said reaction motor whereby a propulsive thrustis produced; the improvement wherein said oxidizer grain comprises amaterial selected from the group consisting of NOBrF LiClO NOF, MgClQ,ZNOF, NO CIO, (N0 (AlClO NOZASFB, NO SbF and NO PF 8. The method ofclaim 7 wherein said fuel grain comprises a material selected from thegroup consisting of metal hydride, tetramethylammonium hydrotriborate,diaminotetrazine, 4-amino-3,5-dihydrazino-l ,2,4- triazole, N H BH, ,u-(hydrazino )decaborane 3,6-dihydrazino-s-tetrazine, NH Ntriaminoguonidinium diazide, (CH NB -,H and B l-l 2Nl-l

2. The process of claim 1 wherein said oxidizer grain contains anignition aid comprising an alkali metal hexafluorobromate.
 3. Theprocess of claim 1 wherein said oxidizer grain contains from 5 to 12percent by weight of a totally fluorinated polyethylene resin.
 4. Ahypergolic solid oxidizer grain consisting essentially of 64% NO2ClO4,27% CsBrF6 and 9 percent totally fluorinated polyethylene.
 5. Theprocess of claim 1 wherein said fuel grain comprises a material selectedfrom the group consisting of metal hydrides, tetramethylammoniumhydrotriborate, diaminotetrazine, 4-amino-3, 5-dihydrazino-1,2,4triazole, N2H4(BH3)2, Mu -(Hydrazino) decaborane,3,6-dihydrazino-s-tetrazine, NH4N3, triaminoguanidinium diazide,(CH3)4NB3H8 and B10H12 . 2NH3.
 6. The process of claim 5 wherein thefuel grain contains up to 50 percent by weight of polyethylene as abinder.
 7. In a method for producing thrust from a reaction motor whichcomprises providing a solid oxidizer grain and a solid fuel grain withinsaid reaction motor, said oxidizer and said fuel being members of anacid base pair capable of generating sufficient energy from an acid basereaction to active an oxidation-reduction reaction between said oxidizerand fuel; placing said oxidizer and fuel grains in intimate contactwithin said reaction motor for sufficient time to initiate saidoxidation-reduction reaction whereby gaseous combustion products areproduced within said reaction motor and exhausting said gaseouscombustion products from said reaction motor whereby a propulsive thrustis produced; the improvement wherein said oxidizer grain comprises amaterial selected from the group consisting of NOBrF4, LiClO4 . NOF,MgClO4 . 2NOF, NO2ClO4, (NO2)3 (AlClO4)6, NO2AsF6, NO2SbF6 and NO2PF6.8. The method of claim 7 wherein said fuel grain comprises a materialselected from the group consisting of metal hydride, tetramethylammoniumhydrotriborate, diaminotetrazine, 4-amino-3,5-dihydrazino-1,2,4-triazole, N2H4(BH3)2, Mu -(hydrazino)decaborane,3,6-dihydrazino-s-tetrazine, NH4N3, triaminoguonidinium diazide,(CH3)4NB3H8 and B10H12 . 2NH3.